Clamp for cables or the like



Oct. 6, 1931.

A. O. AUSTIN CLAIP Fon cAaLEs'oR 'ma LIxn Filed Feb. 12. 1929 eqINVENTQR Arf/wr 0. Ausf/fz Bydf /MMK ATTORNEY ur* 'df/ Patented Oct. 6,1931 Search Heem UNITED STATES PATENT OFFICE ARTHUR O. AUSTIN, OF NEARBARBERTON, OHIO, ASSIGNOR, BY MESNE ASSIGNMENTS, TO THE OHIO BRASSCOMPANY, OF MANSFIELD, OHIO, A CORPORATION OF NEW JERSEY CLAMP FORCABLES OR THE LIKE Application led February 12, 1929.

This invention relates to clamps for holding the conductors ofelectrical transmission lines or other strands or cables subjected torelatively high mechanical tension and has for one object the provisionof a clamp of the class named in which the gripping action will bedistributed substantially uniformly throughout an extended portion ofthe cable and in which the various strands composing the cable will beheld against the movement relative to one another.

A further object is to provide a clamp in which holding is effected by asnubbing action distributed along a portion of the conductor, thesnubbing action at any point along said portion being inverselyproportioned to the tension in the cable at such point.

Other objects and advantages will appea` from the following description.

The invention is exemplified in the combination and arrange-ment ofparts as shown in the accompanying drawings and described in thefollowing specification, and it is .more particularly pointed out in theappended claims.

In the drawings:

Fig. 1 is aside elevation of a conductor clamp showing one embodiment ofthe present invention.

Fig. 2 is an elevation looking from the right in Fig. 1.

Fig. 3 is a section on line 3-3 of Fig. 1.

Fig. 4 is a fragmentary elevation of a portion of a modified form ofconstruction.

Fig. 5 is a section on line 5 5 of Fig. 1.

Fig. 6 is a fragmentary elevation of another portion of the modifiedconstruction.

Fig. 7 is a section on line 7 7 of Fig. 6.

In clamps for holding electrical conductors, particularly those used onhigh tension transmission lines where it is desired to maintain a highmechanical tension in the conductor without damage to the same, it isexceedingly difficult to provide the necessary gripping means forholding the conductor. This is particularly true in conductors such assteel reinforced aluminum conductors or hollow conductors either with orwithout a spacer member to prevent collapsing.

In my previous patent, No. 1,002,113, a,

Serial No. 339,304.

form of clamp is shown in which the conductor` enters a. curved seatused for taking up a portion of the stress by snubbing before the finalgrip members act to apply the necessary friction for withstanding theremaining stress. In clamps of this type, it is seldom possible todevelop more than 30% of the grip in the snubbing portion. Where verylarge sized conductors are used, composed of many layers, it isexceedingly difficult to apply enough pressure by the gripping means tohold the inner layers in order to develop the approximate ultimate ofthe conductor. It is therefore, desirable with this class of conductorsgreatly to increase the grip or friction in the snubbing ortion of theclamp. Where the holding is e ected largely by the snubbing portion ofthe clamp, the tension in the conductor, particularly that in the coreof a steel reinforced aluminum conductor, will produce pressure betweenthe inner and outer layers of the conductor so that friction will bedeveloped between these layers and the va.- rious layers will be heldagainst relative movement.

Vhile the incoming conductor, from the transmission line, lies in theaxis of the strain insulator used for supporting and insulating theclamp and conductor from the tower, it is necessary to continue the leador conductor past the insulator either to apparatus or to a clampplace-d in similar manner on the opposite side of the tower. In general,this jumper or portion of the conductor leading past the supportinginsulator is brought downward at an angle from the incoming conductor.The angle between the incoming conductor and uniper is usually greaterthan 900.

It is evident that a clamp may be built up having a helical groove withuniform radius. A clamp made up in this way, however, would be muchlarger than needed and would have a greater' reactive effect andconsiderably more weight for a given grip. In the present invention itis desired to design an eflcient clamp taking the greatest possibleadvantage of the snubbing friction without endangering the conductor.

In general, the snubbing friction exerted by the clamp between twospaced points on the conductor, depen-ds upon the angle between theportions of the conductor at these two points. It is, therefore,desirable to include as large an angle as practical between the portionsof the conductor at the point where it enters the clamp. and the portionat its exit. The pressure produced at any point between the conductorand the clamp will be directly proportional to the tension in theconductor at that point and inversely proportional to the radius ofcurvature of the clamp seat at that point.

In order to prevent the conductor from bearing too hard upon the clampseat and to prevent one portion of the conductor from bearing too hardupon another portion, such as the steel core upon the soft outer layerof aluminum, all that is necessary is to use a curvature at any givenpoint having a given conductor tension of sufficient radius to reducethe pressure to the desired amount. As the conductor progresses alongthe snubbing groove or seat in the clamp, the tension in the conductorwill be transferred to the seat in the clamp and will thereby bereduced. If advantage is taken of this reduction in tension, it ispossible to decrease the radius of curvature of the seat so that thetotal snubbing angle from the point of entry may be gained with ashorter length of seat than would be possible if a uniform radius ofcurvature were maintained and, in addition, the grip may beapproximately the same for equal lengths of the seat. To take advantageof the reduction in tension and maintain uniform snubbing throughout theclamp seat, the seat may follow the contour of a logarithmic spiral. IfT2 represents the tension in the incoming conductor and T1 the tensionor friction developed by the grip members at the inner end of thesnubbing seat, the hyperbolic log of In the above equation f is thecoefficient of friction and n is the angle in degrees included in theseat divided by 360. The above equation holds true for any size ofconduct-or and in order to lay out a clamp, all that is necessary is todecide upon the minimum radius possible at the point of entry for agiven conductor. The effective coeiiicient of friction f will dependupon the conductor as well as upon any wedging action in the clamp seatwhich may be regarded as increasing the effective coefficient offriction. lVhile the coefficient of friction is not increased, thewedging action increases the pressure for a given tension which isequivalent to increasing the effective coeficient for design purposes.By utilizing the above principle, it is possible to develop very highsnubbing frictions in the clamp seat, thereby permitting very lightclamping means in order to develop a high tension in the conductor.

If T2 is the tension in the conductor entering the clamp and 'I1 is thefriction developed by the gripping members, it is frequently possible toso design the clamp that the ratio of T2 to T1 may run from 2% to 5,depending upon the effective coefficient and the amount of wedgingproduced in the seat. In other words, the friction produced by theclamping members may be multiplied from 21/2 to 5 times in most designs.It is, of course, possible to change these limits very materially byincluding a larger snubbing angle or in special cases.

In the form of the invention shown in the drawings the enteringconductor 10 traverses a groove or seat 11 in the clamp body 12 which isequipped with ears 13 for attachment to an insulator string or othersupport. The conductor 10 traverses the curved seat 11, which has acontinuously decreasing radius, until the grip member or clamping piece14 is reached. The clamping piece 14 is pressed against the conductor 10by tightening the nuts 15 which are placed on U-bolts 16 or othersuitable holding means. In some cases an additional clamping piece 17 isused in order to produce additional friction and guide the conductorupon leaving the clamp. The groove 11 in the clamp produces a completeturn and passes itself at one side at the point 18.h The portion of theseat near the grip members 14 is usually displaced slightly from thatwhich would be developed by a true logarithmic spiral in order toprovide the proper clearance for the grip members and to keep the clampas small as possible. lVhere very heavy currents are encountered, it maybe advisable to use a non-magnetic material or a material of highconductivity so that heating will be reduced to a minimum.

As the conductor, in following the clamp seat, makes a complete turn,there will be a tendency for the current flowing in the conductor toinduce an opposite current in the short circuit turn formed by the clampbody if the portions of the body are connected where they cross eachother. There will also be a tendency for a portion of the current toleave the conductor and flow directly to the crossing portion throughthe clamp body without following the loop formed by the conductor. Thismay have a tendency to produce heat where the current leaves theconductor and enters the clamp seat which, in some cases, may beobjectionable. It is usual to place a lining in the seat of the clampmade of sheet aluminum or other suitable soft metal and, in some cases,it may be desirable to place "i" .-1. u www."

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at the point 21. As the voltage at these points will be very small, itis possible to use insulation such as fibre or asbestos which willwithstand the weather and have the necessary mechanical strength. Aslight amount of heat generated in the clamp is usually an advantage asit tends to prevent the formation of sleet and keeps all parts dry,insuring the best possible working conditions in order to insure a longlife in the conductor and hardware.

In a clamp such as that shown in Fig. l, danger from crystallization ordamage to the strands of the conductor is reduced very materially overone where the conductor is griped by a socket, sleeve or other means inwhich the axis of the conductor and clamp are a straight line throughoutthe length of the gripping means. In a clamp such as that shown in Fig.l, it is evident that such a large part of the load is taken up in thesnubbing portion that a tension in the conductor which would reduce itin diameter could not possibly aifect the diameter of the conductor andits grip for any great distance along the seat. Since the effectivenessof the grip in the clamp depen-ds upon the tension and the snubbingangle to a very large extent, it is seen that even tensions which willreduce the diameter of the conductor at the point of entry will notalfect the gripping efficiency of the clamp. In clamps where snubbing isnot possible, but grip is obtained by direct pressure, it is seen thatreduction in cross section due to tension may tend to relieve the gripat the point of entry, thereby transferring` the full tension to agreater distance in the clamp. Since tension in the conductor reducesits diameter radially, it is seen that it is not advisable to placecompression normal Yto the axis of the conductor until the stress ortension in the conductor is reduced. Otherwise, the tendency to deformthe conductor in addition to the deformation due to tension, will beincreased.

In dead-end or strain construction, particularly where very highvoltages are used, the limit in flashover voltage for the installationis usually determined by the voltage at which a discharge will takeplace from the jumper to the supporting structure. This can always bemade the limit for any structure as it is possible to increase thelength of the strain or dead-end insulator sufliciently to cause ashoverbetween jumper and tower. A strain or dead-end tower differs materiallyfrom a suspension tower in this connection. If therefore, the flashovervoltage between the jumper and the structure can be increased over thatin a normal installation, it is possible to obtain higher insulation bysimply lengthening or increasing the strain insulators. In doublecircuit towers or where the conductors are placed on the outside of thetower, it is possible greatly to increase the effective clearance of theconductor by utilizing the clamp to hold the jumper 22 at a distancefrom the structure. In other words, the jumper may be held not onlydownward, but outward from the tower as well, or even upward in the caseof the center phase in a fiat single circuit construction or itsequivalent.

In many cases the jumpers have caused serious trouble owing to the factthat they did not have sulicient clearance from the structure or swunginto the structure during heavy winds. In many installations it has beennecessary to stiffen or hold the jumpers by angle construction whichgreatly increases the mass attached to the conductor, forms sharp anglestending to cause discharge and is generally objectionable.

In the present type of clamp, a support or brace for holding the jumpercan be readily attached. Such an extension or holding member 23 is shownattached to the body of the clamp and gripping the jumper by a clamp 24.This extension member may be in any form desired and extend for aconsiderable distance from the clamp so as to insure clearance for theconductor.

I-Iolding the jumper may also be of material advantage in that anyvibration or oscillation in the clamp will tend to set up frictionbetween the strands in the jumper, thereby tending to dampen outoscillations. This is particularly true where the holding member on thejumper extends for some distance from the clamp, tending to magnify anymovement.

It will be understood, of course, that where the slack end of theconductor is not continued past the clamp to form a jumper, the exit endof the clamp need not be shaped to give a particular direction to theslack end of the conductor. In a case of this kind, it may not benecessary or desirable to continue the seat at its exit end beyond thecontour of the adjacent lap. Of course, the slack end of the cable willbe secured to the clamp in some suitable manner but if the end is notcontinued to form a jumper, the final gripping portion of the clamp maydiffer from that shown in the drawings where the arrangement is designedto give a particular direction to the slack end of the cable.

In order further to absorb oscillations, an extension member 25 isattached to the body of the clamp at 26 and 27 by suitable clampingmeans. A frictional device 28 rides over a complementary sleeve ormember 29 so that any movement between the members 28 and 29 will causedissipation of energy which will tend to absorb vibrations. The meansused for producing this dissipation of energy may vary considerablywithout changing the principle involved. The action is similar to thatof a shock absorber used in automotive practice and, in fact, devicesinvolving constructions similar to those of shock absorbers might beattached at this point, particularly those equipped with arms arrangedso that any relative movement between the conductor and the member 25would cause relative rotation of frictionally engaging parts with aconsequent dissipation of energy. In many cases, however, the frictionalmeans can be quite simple as a slight dissipation of energy will dampenout oscillations which will damage the conductor. The amount of frictionrequired and the length of arm and stiffness of the member 23 will, ofnecessity, depend upon the conductor and conditions under which it isinstalled. Where greater relative movement is desired, it is necessaryto extend the arm, or place the rubbing surfaces Where the amplitude ofoscillation tends to be large.

I claim:

l. A cable clamp comprising a snubbing member having a curved seat forreceiving the cable, said seat being disposed in a loop, the axis ofwhich is substantially normal to the load end of the cable, the load endof said cable extending away from said seat in a direction substantiallytangent to the curvature of said seat, means for securing a support tosaid clamp substantially in alignment with the load end of said cable,the radius of curvature of said seat being decreased progressively, saidseat being extended to form more than a complete turn and having asubstantially straight portion extended from the end thereof, havingthey lesser radius of curvature, said straight portion being directedaway from the load end of said cable at an oblique angle to said cable,and means for securing said cable to said straight portion of said seat.

2. A cable clamp comprising a curved cable seat having any entrance endfor receiving the load end of a cable and an exit end from which theslack end of said cable extends, said seat being curved about alprogressively decreasing radius from the load end to the. exit endthereof, thus forming a loop, the axis of which is substantially normalto the load of the cable, means for clamping said cable to said seatadjacent said exit end, and an extension secured to the exit end of saidseat for directing the slack end of said cable away from said seat.

3. A cable clamp comprising a cable seat having an entrance end forreceiving the load end of a cable, a holding member for said clamparranged substantially in alignment with said cable where it enters saidseat, said seat being curved away from the axial line of said cableforming a loop, the axis of which is substantially normal to the loadend of the cable and providing a snubbing surface having a progressivelydecreasing radius of curvature, the curvature of said seat beingextended for more than 360, .and means for clamping the slack end ofsaid cable to said seat adjacent the portion of said seat having thelesser radius of curvature.

4. A cable clamp comprising a body member having a curved cable seatprovided with an entrance end for receiving the load end of the cableand an exit end from which the slack end of the cable extends, said seatbeing disposed in a loop, the axis of which is substantially normal tothe load end of the cable, means for securing a holding member to saidclamp substantially in alignment with the load end of said cable, saidseat being curved through more than 360O to direct the slack end of saidcable away from the load end of said cable at an oblique angle to saidload end.

5. A cable clamp comprising a body member having a cable seat providedwith an entra-nce end for receiving the load end of a cable and an exitend from which the slack end of the cable extends, said seat beingdisposed in a loop, the axis of which is substantially normal to theload end of the cable and following a curve at one side. of the axis ofthe load end of said cable, the radius of curvature of whichprogressively decreases from the load end to the exit end of said seat,means for securing said cable to said clamp adjacent the exit end ofsaid seat, said seat being extended through a complete turn, and meansfor securing a. holding member to said clamp substantially in alignmentwith the axis of the load end of said cable.

6. A cable clamp having a snubbing seat substantially in the form of alogarithmic spiral, the load end of said cable entering said seat at theend thereof having the greater radius of curvature while the slack endof said cable extends from said seat at the end thereof' having thelesser radius of curvature, the logarithmic curvature of said seat beingcontinued outwardly substantially to the end of said seat at the pointof entrance of said cable, means for securing the slack end of saidcable to said clamp, and a support for said clamp arranged substantiallyin alignment with the load end of said cable.

7. A cable clamp having a snubbing seat curved to form more than acomplete turn, adjacent portions of the different laps of said seatbeing mechanically attachedbut electrically insulated from each other attheir crossing.

8. A cable clamp comprising a cable scat having its entrance endsubstantially tangent to the load end of said cable and having asupporting portion substantially in alignment with the load end of saidcable, said seat being curved away from the axis of the load end of saidcable upon a curve having a progressively decreasing radius ofcurvature, said seat making more than one complete turn and beingprovided with an exit portion directed away from the axis of the loadend of said cable at an oblique angle thereto, said exit portion beingoffset lateral- 1y to pass the adjacent lap of said seat, means securedto said exit ortion for directing the slack end of said ca le, means forclamping said cable to said seat adjacent the exit end thereof, avibration damping device secured to said clamp adjacent the entrance endthereof and engagingr the. load end of said cable to damp out vibrationsthereof, and means for insulating adjacent portions of the differentlaps of said seat from each other.

In testimony whereof I have signed my name to this specification this9th day of February, A. D. 1929.

ARTHUR O. AUSTIN.

